Caption: La Silla telescope domes at sunset. The European Southern Observatory's (ESO) site at La Silla, Chile, has telescopes which observe at optical, infrared and radio wavelengths. The largest optical telescope has a mirror with a diameter of 3.6 metres, whilst the largest radio telescope has a dish with a diameter of 15 metres. The high altitude of La Silla (2400 metres), and the clear air above it (reducing atmospheric distortions of incoming light), make the site an ideal location for astronomical observations.